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Introduction Diuretic failure is a potential life-ending event but is unpredictable and poorly understood. The objectives of this study were to evaluate pharmacodynamic markers of furosemide-induced diuresis and to investigate mechanisms of diuretic braking in dogs receiving constant rate infusion (CRI) of furosemide. Animals Six healthy male dogs. Methods Raw data and stored samples from one arm of a previously published study were further analyzed to mechanistically investigate causes of diuretic braking in these dogs. Urine volume was recorded hourly during a 5-h furosemide CRI. Urine and blood samples were collected hourly to measure serum and urine electrolytes, urine aldosterone, and plasma and urine furosemide. Serum electrolyte fractional excretion was calculated. Urine sodium concentration was indexed to urine potassium (uNa:uK) and urine furosemide (uNa:uFur) concentrations, plasma furosemide concentration was indexed to urine furosemide concentration (pFur:uFur), and urine aldosterone was indexed to urine creatinine (UAldo:C). Temporal change and the relationship to urine volume were evaluated for these measured and calculated variables. Results Urine volume was significantly correlated with urine electrolyte amounts and with uNa:uK. The ratio of pFur:uFur decreased during the infusion, whereas furosemide excretion was unchanged. Conclusions There was a strong relationship between urine volume and absolute urine electrolyte excretion. Urine volume was strongly correlated to uNa:uK, giving it potential as a spot indicator of urine production during diuresis. The decrease in uNa:uK over time during the infusion is consistent with mineralocorticoid modification of urinary electrolyte excretion, supporting renin–angiotensin–aldosterone activation as a cause of diuretic braking in this model. [ABSTRACT FROM AUTHOR]

Objective The goal of this study was to investigate the short-term safety and diuretic efficacy of furosemide constant rate infusion (CRI) diluted with 5% dextrose in water (D5W) compared to dilution with 2.4% hypertonic saline in healthy dogs. Animals Six healthy dogs. Methods Dogs were studied in a randomized, blinded, crossover manner. Furosemide 3.3mg/kg was diluted to 2.2mg/mL with either 1.5mL/kg D5W for the DEX method or with 1.0mL/kg D5W and 0.5mL/kg of 7.2% hypertonic saline for the H-SAL method. After a 0.66mg/kg furosemide IV bolus, the infusion rate was 0.3 mL/kg/hr for 5 h such that both methods delivered 0.66 mg/kg/hr (total 3.3mg/kg) furosemide in equal volume for the study duration. Urine output, water intake, central venous pressure (CVP), physical parameters, furosemide concentrations, blood and urine electrolytes, and urine aldosterone to creatinine ratio (UAldo:C) were evaluated. Results Measured variables were not different between methods but showed changes over time consistent with diuresis. Mean CVP decreased over time similarly for both methods. Plasma furosemide and urine concentrations were stable and not different between methods. Both furosemide CRI methods showed an increase in the UAldo:C, however, the rise was greater for DEX than for H-SAL. Conclusions Diuresis was similar for both furosemide CRI methods; however, the H-SAL method induced less renin-angiotensin-aldosterone system activation than the DEX method. The absence of intravascular volume expansion based on CVP suggests that dilution of a furosemide CRI with 2.4% hypertonic saline may be well tolerated in heart failure. [ABSTRACT FROM AUTHOR]